ABSTRACT Overweight/obesity is a significant epidemic afflicting a majority of Americans, some of whom develop insulin resistance (IR), which contributes to the development of type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD). It remains a critical question why some individuals develop IR at modestly elevated body weight and others can sustain substantial amounts of excess body fat while remaining insulin sensitive (IS). Prior studies using GWAS have failed to fully explain this phenomenon. Focusing strictly on genetics, however, misses the complex and lifelong effects of diet and environment on cellular function. To gain a more complete picture of the IR process, our group proposes to apply a longitudinal multi-omic strategy of unprecedented depth for the discovery of molecular changes associated with the development of IR using a human model for experimental weight gain, followed by weight loss. We will measure biomolecules (transcripts, metabolites, proteins and cytokines) in blood, adipose tissue, and muscle: 1) at baseline comparing IR to IS Individuals; 2) at peak weight as compared to baseline and post weight loss; 3) compare changes in those individuals who experience metabolic decline with weight gain vs those who exhibit metabolic tolerance of similar weight gain. We hypothesize that through this dynamic intervention with longitudinal analysis we can elucidate biomolecules and pathways that change in response to weight gain and loss and specifically that uniquely associate with IR independent of weight or weight gain. These highly novel data that can be generated only by our group will significantly expand our understanding of biomolecules and pathways that characterize and predict development of the IR state, offering new markers for enhanced risk stratification (for adverse response to weight gain) and therapeutic strategies that have potential for a major impact on preventing obesity-induced metabolic disease.